Spark plug



Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE SPARK PLUG Application June 22, 1933, Serial No..676,996

3 Claims. (Cl. 12S-169) My invention relates to spark plugs for internal combustion engines, of the usual type wherein a central electrode extends through a passage in an insulator made of porcelain or equivalent ceramic material, and which insulator is assembled within the 'external metallic shell of the plug; and the object thereof is to provide certain central electrode and insulating member features whereby the insulating member is l@ strained less, and is less likely to be broken during the assembling of the central electrode therewith and the securing of it in place, than has heretofore commonly beenV the case in spark plugs.

A further object of my invention is to provide s. spark plug with insulating member and central electrode features whereby a more rapid and .effective dissipation of heat therefrom and to the metallic shell of the plug occurs than has heretofore been the case in spark plugs' having similar central electrode features; and with features wherein such expansion of the central electrode (due to the heating thereof by burning gases within the engine cylinder) as cannot be prevented will not injure the insulating member, as by setting up strains therein acting to crack or otherwise injure the same.

With the above and other objects of invention hereinafter appearing in view, my invention consists in the improvedcentral electrode and insulating member features illustrated in the accompanying drawing and hereinafter described andclaimed; and in such modifications and variations thereof, within the scope of the concluding claims, as will be obvious to those skilled in the art to which my-invention,relates.

In the drawing wherein the preferred form of my invention is illustrated:

Figure 1 is a view showing a section upon a 40 longitudinal central plane, of a spark plug wherein the features in which my invention consists are present.

Figure 2 is a similar View, the shell of the plug being omitted, showing my invention in a slightly modified form. Both figures show the parts about three times their actual size. l

Referring now to the drawing for a more complete understanding of my invention, the numeral 5 designates the external metallic shell or 5o casing of'a spark plug; and 6 the insulating member of porcelain or equivalent material which is secured within the shell in any of the waysv commonly employed in spark plugs for that purpose. The insulating member in the preferred form of my invention illustrated has an enlarged central portion for convenience in securing it in place within the outer shell of the plug although my invention is not limited to an insulating member having that feature, nor to a plug wherein the insulating member is secured within the shell 00 in the particular manner illustrated.

The insulating member has an internal ledge 7 located, preferably, within the enlarged central part thereof; an electrode passage 8 leading from said ledge to the inner end thereof; and a larger passage 9 extending from said ledge to the outer end of the insulating member. This last passage is provided with an internal thread or equivalent feature whereby a terminal electrode and holding member l0 may be interlocked with the insulating member in a positive manner and held inplace in said larger upper passage, and if as shown an internal screw thread is employed for that purpose the passage may be threaded throughout its length as shown in Figure 1, or at its inner end only as shown in Figure 2. In fact the particular manner in which the member 10 is interlocked with the insulating member 6 may be varied so long as the means whereby such interlocking is accomplished is within the enlarged upper passage 9 when the parts are assembled.

The numeral l1 designates the central insulated electrode of the plug, the same having an enlarged head l2 at its inner end and which 85 head rests upon the ledge 7. This electrode extends through the passage 8 and fits closely therein, the passage being larger than the electrode only to an extent sufficient to permit the electrode to be conveniently assembled with the insulating member. The electrode is loose in the passage, that is no cement is present between it and the interior wall of the passage; from which feature it results that the electrode is free to expand independently of the insulating member as it becomes heated, and that expansion and contraction thereof does not subject the inner end of the insulating member (which expands very much less than the metallic electrode) to strain as would be the case if the electrode was cemented in place within the passage through which it extends.

The inner end of the terminal and holding member l0 engages the head l2 when the parts are assembled and holds said head in engagement with the ledge '7, and the electrode 11 in place in the passage 8. A small quantity of cement is commonly supplied to the passage 9 after the electrode is put in place and which, when the terminal member is in place, provides a 110 ido seal at 13 about the head and the lower end of said member. Some of this cement will be forced inw the interstices between the threads at the lower part of the member 10 and the internal threads of the passage 9 (or between the parts of whatever form of interlocking elements are made use of) as the terminal and holding member is moved into its assembled position, thereby providing a more perfect and effective seal; and cement may be thereafter supplied, as shown at 14, to the space between the reduced upper part of this member and the interior of the passage 9;4 this last cement, if present, being supplied after the inner end of said member has been cemented in place as hereinbefore explained. The outer end of the member 10 is threaded as shown at 15 to receive the usual terminal nut for connecting an electrical supply cable to the inner electrode of the plug, and the inner end thereof is shown as rounded at 16 to avoid side thrust upon the head 12 if, as sometimes happens, the axes of the passages 8 and 9 are not parallel and in alignment with one another. The lower end of the member 10, though in contact with the head so as to provide a metallic conducting path for a current of electricity, is not continuous with the lower electrode, from which it follows that the assembling of the parts will not subject the insulating member, particularly the inner end thereof, to strain tending to break or otherwise injure the insulator.

In the form of my invention illustrated in Figure 2, the passage 17 is threaded only at its inner end, and the terminal and holding member 18 is tubular, and has holes or slots 19 at its lower end;

and after the electrode and the holding member have been assembled a suitable cement is supplied under pressure to the interior of said member, which cement flows through the slot 19 and rises between the threads or equivalent interlocking elementsv and forms a seal 20 between the holding and terminal member and the passage 17 through which it extends. In this form of my invention the outer end of the member 18 is shaped to receive the spring clip of a supply cable instead of threaded to receive a nut as in Figure l.

In the preferred form of my invention illustrated the head 12 of the electrode 1l lies within the enlarged central part of the insulating member 6 as does also the inner part of the member l0 (or 18) which is in direct and intimate contact with the interior of the passage 9 (or 17), and the two are in direct metal to metal contact. It therefore follows that heat derived from the burning gases and flowing along the electrode l1 is conducted to comparatively massive metal parts, and that a large part thereof is distributed f is throughout the massive central part of the insulating member and flows to the shell of the plug and is dissipated to the atmosphere and to the head and water jacket of the engine. The features, therefore, wherein my invention consists secure a more eective conduction of heat from the inner electrode element, and a more rapid dissipation thereof to theshell ofthe plug than has heretofore been secured in spark plugs of the type to which my invention relates.

In the making of spark plugs the porcelain or equivalent material insulating members are made into their nal shape, and the passag 8, 9 and the ledge 'l are provided, before the members are glazed and fired. The material being quite soft it follows that the passages are often not perfectly formed, and are not always parallel and in alignment; and these andother imperfections are nal member, the assembly thus produced is likely to be more or less crooked or otherwise out of shape as when the axes of the two do not coincide. Thus and unless the parts approach very nearly to perfection the assembling thereof is more or less difficult, and is often accompanied by bending of the metallic electrode and in the setting up of stresses which often break the insulator; this injury to or destruction of the insulator often occurring after the plug is finished as the strains produced may not be followed by immediate failure of the insulating member. A quite common way of attempting to avoid strains in the insulating member has been to make the passage for the lower end of the single piece central electrode structure much larger than the electrode; but this necessitates the lling of the passage around the same with cementA thus introducing a condition wherein longitudinal expansion of the electrode,

due to heating thereof when the plug is in use,

is liable to break the lower end of the insulating member; because, as will be appreciated, the material of the insulating member has a negligible coeilicient of expansion and expands little if at all, while the metallic electrode expands appreciably when the plug is heated by the burning gases within the combustion chamber of the engine.

In my invention and because the lower part of the central electrode structure is independent M0 of the upper part, the two may be assembled in passages which may be considerably out of alignment or otherwise lacking in perfection, without straining either electrode part or setting up stresses in the insulating member. Furthermore and as will be appreciated, the passage for the lower electrode proper (the part 8) may be made of lesser diameterthan heretofore, in fact only sumciently` larger than the electrode to permit the same to be put in place, thus making it unl2@ necesry to surround such lower part with cement and avoiding injury tothe insulatingv member by longitudinal expansion of said electrode as the plug becomes heated; and the fact that a comparatively short length only of the terminal 125 and holding member 10 (or 18) is threaded and rigidly interlocked with the insulating member lessens the liability to injury at this part of the insulator due to such expansion as may occur in said short length of the member 10 (or 18) due '130 to the heating of such part by conduction from the head 12 of the electrode 11. As a matter of course the inner threaded end of the terminal and holding member 10 (or 18) does not attain anything like the temperature of the electrode ll, 135 because the greater part of the heat is dissipated to the plug shell and engine structure; but nevertheless a decided advantage as regards the avoidance of strains in the insulating member is secured by making this threaded part short as compared with the total length of said member.

Having thus described and explained my invention I claim and desire to secure by Letters Patent: v A

' l. In a spark plug, an insulating member having an enlarged central portion, an internal ledge within said enlarged portion, a passage leading from -said ledge to the inner end of said insulating member, and a larger internally threaded passage leading from said ledge to the outer lend -lif of said insulating member; an electrode extending through said first-mentioned passage and having an enlarged head which rests upon said ledge; and a threaded terminal and holding member extending through said larger passage. and the lower end of which is rounded and engages the head aforesaid to hold said electrode in place.

2. Lin a spark plug, an insulating member having an internal ledge, a passage leading from said ledge to the inner end of said insulating member, and a larger internally threaded passage leading from said ledge to the outer end of said insulating member; -an electrode extending through said mst-mentioned passage and having an enlarged head which rests upon said ledge; and a tubular threaded terminal and holding member extending through said larger passage, and the lower end of which engages the head aforesaid to hold said electrode in place.

3. In a spark plug, an insulating member having an internal ledge, a passage leading from said ledge to the inner end of said insulating member, and a larger internally threaded passage leading from said ledge to the outer end of said insulating member; an electrode extending through said first-mentioned passage and having an enlarged head which rests upon said ledge; a tubular terminal and holding member extending through said larger passage and Aabutting against said head to hold said electrode in place; and means upon said terminal and holding member and within said larger passage adapted to interlock, to thereby secure said member in place within said larger passage.

HECTOR RABEZZANA. 

